The redox chemistry of isolated functional groups is appreciably different from the situation where two or more groups strongly interact. The first part of this proposal describes a plan to determine the influence of intramolecular interactions on electron transfer processes associated with the oxidation of thioethers, the stability of aliphatic thioether cation radicals and dications, and the reduction of sulfoxides. Compounds with medium-sized rings (7 to 10 members) in which the thioether group is located across the ring from a lone pair donor are the best model systems to use to study the interaction. The lone pair donors used are representative of the functional groups found on common amino acid side chains. Both chemical and electrochemical methods will be utilized to examine the redox chemistry of each of the molecules prepared. The second part describes a study of the interaction of the thioether group with copper (II). This study is significant since the thioether group of methionine is often present at the active site of enzymes engaged in electron transfer. Of paramount importance is a study of the conditions necessary for copper (II) to oxidize rather than simply coordinate to the thioether. We will also search for additional examples of mixed-valence copper complexes of thioethers. We also plan to study the correlation of electronic structure with the type of donor atoms and the geometry of copper. Previous correlations have been shown to be incorrect due to variations in association of monomeric units in the solid state. The X-ray crystal structures of molecules having the same donor sets but different intramolecular association will be obtained. The kinetics of the reduction of copper (II) by thioethers will also be investigated.